A diving suit gives the diver a good protection against getting cold and other factors (like sharp rocks). They come in different thickness for different watertemperatures. A good choice for tropical destinations will be a 3mm diving suit, for watertemperatures between 23 and 27 degrees a 5mm diving suit and for below 23 degrees a 7mm diving suits. Also different types of diving suits exist, a diving suit with short arms & legs is called a "Shorty" and diving suit with long arms & leggs is called a "Longy".